Lizard myogenic culture lineages have been maintained at 80-90 percent diploid for over 1,000 generations. By a variety of criteria they are not transformed. The lizard myogenic system is a striking exception to the Hayflick hypothesis of cellular aging in vitro. We propose to test the generality of the Hayflick hypothesis in a lower vertebrate, Anolis carolinensis. We are asking the following questions: 1) is the unlimited proliferation potential of lizard myogenic stem cells unique to muscle or is it a property of all lizard cells? 2) Is the observed unlimited proliferation potential of myogenic stem cells a consequence of our culture regime and our ability to select for 'normal' cells?